In many generators such as high speed generators utilized in aircraft, it is highly desirable to eliminate brushes since they frequently require maintenance and/or replacement and are perhaps the single weakest point in the system in terms of breakdowns. Moreover, by its very nature, the electrical path between a brush and a commutator is subject to arcing which may introduce transients into the electrical energy being produced which in turn may interfere with proper operation of some types of electrical loads on the generator.
A typical brushless generator has three distinct generating systems, including a main generator, an exciter and a permanent magnet generator. The permanent magnet generator includes rotatable permanent magnets for establishing a magnetic field which is electrically employed to induce current in a set of stationary windings which in turn is employed after rectification and voltage regulation to generate a magnetic field in the exciter. The magnetic field in the exciter is in turn employed to induce an even higher level of current, typically three phase alternating current, which is then employed after rectification to generate the magnetic field for the main generator by flowing a DC current through a main field winding of the generator system.
In order to avoid the use of brushes, it is necessary that the field winding in the main generator be in the rotor so that the output of the system can be taken from a stator of the main generator. In order to generate a suitable magnetic field in the rotor, it is necessary to utilize direct current as opposed to alternating current for the same. Since the output of the exciter is an alternating current, this current must be rectified by a rectifier assembly to direct current. Again in order to avoid resorting to brushes, it is necessary that the rectifier assembly interconnecting the exciter and the main generator field winding be carried by the rotor of the generator. Such a rectifier assembly should also be capable of withstanding high centrifugal loading. One such rectifier assembly is disclosed in commonly owned U.S. Pat. No. 4,628,219 issued Dec. 9, 1986, to Troscinski.
It is of course desirable in aircraft applications to minimize weight. In the case of brushless generators having a relatively long axial length, because such generators are typically mounted to the engine gear box at only one end of the generator, such generators result in the presence of a relatively large, so-called "overhung" moment. In order to support such a generator, the gear box must be made proportionately stronger than would be the case for a generator having a lesser overhung moment; and that reinforcement will most frequently require the presence of additional undesirable weight. In addition, aircraft applications require that close heed be paid to aerodynamic considerations. These considerations may dictate location of aircraft components in areas where space is at a premium or else an aerodynamic penalty may be felt.
One method of reducing the overall length of a two-pole brushless generator system is disclosed in commonly owned U.S. Pat. No. 4,797,590 issued Jan. 10, 1989 to Raad, et al. Raad disclosed a brushless generator wherein both the permanent magnet generator and the exciter are adjacent one end of the main generator in an essentially coplanar relation with the permanent magnet generator radially inward of the exciter. However, in a two pole brushless generator system where, as is well known in the art, a solid rotor is required, use of the arrangement disclosed in Raad is not feasible.
A way to reduce the overall axial length of a brushless generator system is to reduce the axial length of the rotating rectifier diode package. The package in use now has an axial length greater than three inches This application describes a design of a rectifier assembly which is 1.55 inches long, which presents a decrease in the length of the package.
It is also desirable to provide a way for easily removing a rectifier assembly in the event of a failure.
The present invention is directing to overcoming one or more of the above problems.